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Network - 100BaseT

The general name for any of three 100 Mbps Ethernet variants that have just been made a standard by an IEEE 802.3 subcommittee (802.3u). 100BaseT Ethernet is one of the candidates trying to become the standard 100 Mbps Ethernet. This version was developed and proposed originally by Grand Junction, in collaboration with several other corporations. The term fast Ethernet is often used for this version. This is unfortunate, since that term is also used to refer to any Ethernet implementation that supports speeds faster than the official 10 Mbps standard. To add to the confusing terminology, a software product (no longer available) was also named fastEthernet. 100BaseT Ethernet retains Ethernet's CSMA/CD (Carrier Sense Multiple Access/ Collision Detect) media access method-in contrast to the 100BaseVG variant (now officially, IEEE 802.12)-which is the other major 100 Mbps Ethernet available. The main differences between fast (100 Mbps) Ethernet and standard (10 Mbps) Ethernet are: n A 100BaseT Ethernet allows a much shorter gap between signals. n A 100BaseT Ethernet requires either higher-grade cable or more wire pairs. It can run at 100 Mbps speeds on Category 3 or 4 cable-provided four pairs are available; Category 5 cable requires only two pairs. n Currently, a 100BaseT Ethernet can support a network that is only about a tenth of the length allowed for an ordinary Ethernet network. For networks that use copper (as opposed to fiber-optic) cabling: Two nodes of a 100BaseT4 network can be no further apart than 205 meters-regardless of whether the nodes are next to each other. The following variants of 100BaseT Ethernet have been defined: 100BaseFX: Runs over multimode fiberoptic cable. Nodes on a 100BaseFX network can be up to two kilometers apart. 100BaseTX: Uses two wire pairs, but requires Category 5 unshielded or shielded twisted pair (UTP or STP) wire. 100BaseT4: Can use category 3, 4, or 5 UTP cable. The T4 in the name comes from the fact that four wire pairs are needed: two for sending and two for receiving. In some configurations, fast and ordinary Ethernet nodes can share the same network. Fast Ethernet devices identify themselves as such by sending a series of FLPs (fast link pulses) at startup. PRIMARY SOURCES IEEE 802.3u committee publications BROADER CATEGORIES Ethernet COMPARE 100BaseVG